The invention relates to a piezoelectric resonator comprising a sealed box in which a vacuum has been formed or into which has been introduced a residual gas, within said box a piezoelectric crystal having first and second main opposite faces, a first metal electrode deposited on the first main face of the crystal and a second metal electrode deposited on the second main and opposite face of the crystal, a first conductor connected to the first electrode and extending outside the box, a second conductor connected to the second electrode and extending outside the box and means for maintaining crystal within the box.
The presently known high performance quartz resonators are almost entirely of the type having electrodes adhering to the crystal. In such a resonator, the quartz crystals are conventionally suspended by two or three thin nickel strips, which constitute the connection between the electrodes and the contacts outside the metal envelope or tube constituting the box of the resonator. These thin metal strips, which have both an electrical and a mechanical function, are connected to the quartz by cement, thermocompression bonding, welding, etc. Moreover, in the prior art, it is difficult to precisely locate the suspension points, provide reproducible attachments and prevent inadequately known stresses at the attachment points.
The cavity resonator of the type with electrodes adhering to the crystal has an essential limitation due to the imperfect limiting conditions, i.e. mainly to surface defects limiting the piezoelectric solid and to the suspension of the crystal. Attempts have been made to limit the faults caused by the fixing of the crystal by locating the fixture outside the active part of the crystal, i.e. outside the zone corresponding to that part of the quartz capsule between the electrodes and where the energy is trapped.
However, the fixing of the electrodes to the edge or face of the crystal by thermocompression bonding, cementing or other means is by its very nature discontinuous (for example quartz--metal bonding or presence of a cement) and causes perturbations to which the resonator frequency is sensitive.